Add-On Dev: Button that simply calls a Function?
The following example shows how to create multiple operators each with their specific function. It only shows three buttons, but the concept remains the same for an arbitrary number of buttons and their underlying operators. The panel is created in the sidebar of the 3D View which can be opened with N.

I hope I haven't misunderstood what you're trying to accomplish. In case I did, feel free to leave a comment.

bl_info = {
    "name": "Multiple operator example",
    "author": "Robert Guetzkow",
    "version": (1, 0),
    "blender": (2, 80, 0),
    "location": "View3D &gt; Sidebar &gt; My own addon",
    "description": "Example with multiple operators",
    "warning": "",
    "wiki_url": "",
    "category": "3D View"}

import bpy


class EXAMPLE_OT_func_1(bpy.types.Operator):
    bl_idname = "example.func_1"
    bl_label = "Function 1"

    def execute(self, context):
        # Implement your first function here
        self.report({'INFO'}, f"This is {self.bl_idname}")
        return {'FINISHED'}


class EXAMPLE_OT_func_2(bpy.types.Operator):
    bl_idname = "example.func_2"
    bl_label = "Function 2"

    def execute(self, context):
        # Implement your second function here
        self.report({'INFO'}, f"This is {self.bl_idname}")
        return {'FINISHED'}


class EXAMPLE_OT_func_3(bpy.types.Operator):
    bl_idname = "example.func_3"
    bl_label = "Function 3"

    def execute(self, context):
        # Implement your third function here
        self.report({'INFO'}, f"This is {self.bl_idname}")
        return {'FINISHED'}


class EXAMPLE_PT_panel(bpy.types.Panel):
    bl_label = "My own addon"
    bl_category = "Name of your tab"
    bl_space_type = "VIEW_3D"
    bl_region_type = "UI"

    def draw(self, context):
        layout = self.layout
        layout.operator(EXAMPLE_OT_func_1.bl_idname)
        layout.operator(EXAMPLE_OT_func_2.bl_idname)
        layout.operator(EXAMPLE_OT_func_3.bl_idname)


classes = (EXAMPLE_OT_func_1, EXAMPLE_OT_func_2, EXAMPLE_OT_func_3, EXAMPLE_PT_panel)


def register():
    for cls in classes:
        bpy.utils.register_class(cls)


def unregister():
    for cls in classes:
        bpy.utils.unregister_class(cls)


if __name__ == "__main__":
    register()